Yes, I see cracked and broken iPhones and S3/4/5s all the time too.
I never look for a case for a phone I buy though, I just buy one that is built well.
And it may be true that my case-less phone is treated with less care but it is two years old and almost unmarked, despite many drops and scrapes.
But then it is made from materials like machined monoblock plastic that doesn't tend to show wear and marks as well as being radio transparent, along with thick Gorilla glass that is borderline unbreakable. Screen shield, horrible, ugly.
Every time I see someone walking and talking (or driving) with a giant phone against their head plus dangly case flapping about all over the place I just wonder why they bother paying for the thinner, sexier phone with the less-good battery life in the first place.